1. Technical Field
The present invention relates to oscillation devices, and methods for manufacturing an oscillation device.
2. Related Art
Sensor modules that can detect physical quantity such as acceleration, angular velocity (i.e., motion sensors) are known. A sensor module may include an oscillation device having a sensor element such as a gyro sensor crystal oscillator (a gyro oscillation member) and a semiconductor circuit element for driving the sensor element contained in a base substrate (see, for example, Japanese Laid-open Patent Application 2004-248113) (Patent Document 1). In the process of manufacturing such an oscillation device, the sensor element and the semiconductor circuit element are mounted within a package, and then the sealing step, in which a reduced pressured state or a vacuum state is created within the package (i.e., a degasification process), is performed, using a metal lid member.
As described in Patent Document 1, the sealing step using a metal lid member is performed through welding a seal ring of the package with the lid member. Accordingly, high-temperature process (for example, at 1000° C. or higher), such as, laser welding, seam welding or the like needs to be performed on the oscillation device. However, when the oscillation device is processed with such high temperatures, the constituting members, such as, the ceramic substrate, the lid member and the like may thermally contract with their respective thermal expansion coefficients, which would likely lower the joint reliability among the constituting members. When the joint reliability between the lid member and the base substrate is lowered, the degree of vacuum (the degree of airtightness) within the package may lower and the crystal impedance (CI) of the sensor element may therefore change, which leads to a possibility that the reliability in oscillation frequency of the oscillation device may lower.
In recent years, further downsizing and miniaturization and commercial production of such oscillation devices are in greater demand. For example, downsizing has very much advanced in recent years to the extent that the device size of an oscillation device is aimed for about 1 mm×1 mm, and remarkable miniaturization of the constituting members has achieved.
If a welding technique, such as seam welding that uses roller electrodes in the sealing step, laser welding that uses a laser beam or the like is used on such oscillation devices which are in pursuit of further downsizing, it is necessary to design the size and layout of the oscillation devices in consideration of applicable conditions of the welding device, in order to practically apply such welding, such as, the roller width of the roller electrodes, the spot diameter of the laser beam and the like. Also, the seam welding that uses roller electrodes is difficult to obtain stable welding quality and also difficult to accommodate itself to welding of members in various shapes other than a rectangular shape. The laser welding requires a very high initial investment in plant and equipment. In view of the above, the use of a welding technique on such oscillation devices which are in pursuit of further downsizing would likely hinder future attempts in further downsizing and miniaturization of oscillation devices and commercial production thereof.
Patent Document 1 describes that metal brazing material such as solder may be used, without performing welding in the sealing step. However, when adhesion material with such a low melting point (for example, 180° C.-300° C.) is actually used, the adhesion material may melt at the time of secondary mounting of the oscillation device to a motherboard or the like, and the degree of vacuum within the cavity may be reduced. For this reason, after manufacturing, the reliability of the oscillation device may be lowered because the thermal resistance of the adhesion material used in the oscillation device is low.